[clang] 24faf90 - [Clang] Add AttrDocs entry for OverflowBehavior (#203392)

[via cfe-commits]

Author: Justin Stitt
Date: 2026-06-12T19:06:16-07:00
New Revision: 24faf90b03a16c248764fb7ab33d9e7cb1d39908

URL: https://github.com/llvm/llvm-project/commit/24faf90b03a16c248764fb7ab33d9e7cb1d39908
DIFF: https://github.com/llvm/llvm-project/commit/24faf90b03a16c248764fb7ab33d9e7cb1d39908.diff

LOG: [Clang] Add AttrDocs entry for OverflowBehavior (#203392)

These docs were previously missing.

Fixes: #203322

Signed-off-by: Justin Stitt <justinstitt at google.com>

Added: 
    

Modified: 
    clang/include/clang/Basic/Attr.td
    clang/include/clang/Basic/AttrDocs.td
    clang/test/AST/undocumented-attrs.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index a1e02e1478df1..1745c5a4f4c2a 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -5483,7 +5483,7 @@ def OverflowBehavior : TypeAttr {
   let Args = [IdentifierArgument<"BehaviorKind">];
   let Subjects = SubjectList<[Var, TypedefName, Field], WarnDiag,
                              "variables, typedefs, and data members">;
-  let Documentation = [Undocumented];
+  let Documentation = [OverflowBehaviorDocs];
 }
 
 def Personality : InheritableAttr {

diff  --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 857015e1c7476..59d4b7ef63d9e 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -10052,6 +10052,51 @@ The following aspects are currently supported:
   }];
 }
 
+def OverflowBehaviorDocs : Documentation {
+  let Category = DocCatType;
+  let Content = [{
+The ``overflow_behavior`` attribute provides fine-grained, type-level control
+over how arithmetic operations on an integer type behave on overflow. It may be
+applied to a ``typedef``, to a variable or data member, or to an integer type
+directly, and accepts one of two behaviors as its argument:
+
+* ``wrap``: arithmetic on the attributed type wraps on overflow, using two's
+  complement semantics. This is equivalent to ``-fwrapv`` but scoped to the
+  attributed type, and works for both signed and unsigned types. UBSan's
+  ``signed-integer-overflow``, ``unsigned-integer-overflow``,
+  ``implicit-signed-integer-truncation``, and
+  ``implicit-unsigned-integer-truncation`` checks are suppressed for the type.
+
+* ``trap``: arithmetic on the attributed type is checked for overflow, enabling
+  overflow checks for the type even when ``-fwrapv`` is in effect globally.
+
+.. code-block:: c++
+
+  typedef unsigned int __attribute__((overflow_behavior(trap))) non_wrapping_uint;
+
+  non_wrapping_uint add_one(non_wrapping_uint a) {
+    return a + 1; // Overflow is checked for this operation.
+  }
+
+  int mul_alot(int n) {
+    int __attribute__((overflow_behavior(wrap))) a = n;
+    return a * 1337; // Overflow is not checked and is well-defined.
+  }
+
+The keyword spellings ``__ob_wrap`` and ``__ob_trap`` are equivalent to
+``overflow_behavior(wrap)`` and ``overflow_behavior(trap)`` respectively.
+
+The attribute wholly overrides global flags (``-ftrapv``, ``-fwrapv``,
+sanitizers, and Sanitizer Special Case Lists) for the attributed type. It can
+only be applied to integer types.
+
+This feature is experimental and must be enabled with the ``-cc1`` option
+``-fexperimental-overflow-behavior-types``. For full details on promotion and
+conversion rules, pointer semantics, diagnostics, and interaction with
+sanitizers, see :doc:`OverflowBehaviorTypes`.
+  }];
+}
+
 def MSStructDocs : Documentation {
   let Category = DocCatDecl;
   let Content = [{

diff  --git a/clang/test/AST/undocumented-attrs.cpp b/clang/test/AST/undocumented-attrs.cpp
index c7a2c74631ea2..eeebd7f938644 100644
--- a/clang/test/AST/undocumented-attrs.cpp
+++ b/clang/test/AST/undocumented-attrs.cpp
@@ -69,7 +69,6 @@ CHECK-NEXT:	ObjCPreciseLifetime
 CHECK-NEXT:	ObjCRequiresPropertyDefs
 CHECK-NEXT:	ObjCReturnsInnerPointer
 CHECK-NEXT:	ObjCRootClass
-CHECK-NEXT:	OverflowBehavior
 CHECK-NEXT:	Packed
 CHECK-NEXT:	Pascal
 CHECK-NEXT:	PointerFieldProtection
@@ -91,4 +90,4 @@ CHECK-NEXT:	Visibility
 CHECK-NEXT:	WeakImport
 CHECK-NEXT:	WeakRef
 CHECK-NEXT:	WorkGroupSizeHint
-CHECK-NEXT: Total: 85
+CHECK-NEXT: Total: 84